As is well known, a pick-up arm basically comprises an elongate arm having a headshell attached to one end thereof for carrying a pick-up cartridge and journalled adjacent its other end in a bearing arrangement providing for rotation of the arm about a vertical axis (for movement of the arm across the surface of a gramophone record) and for pivotal movement about a horizontal axis (for enabling the cartridge carrying end of the arm to be raised and lowered with respect to a record surface and for accommodating warp of the record surface). A balance weight arrangement is supported on the end of the arm remote from the cartridge carrying end and serves to balance the weight of the arm forward of the bearing arrangement and the weight of the cartridge mounted in the headshell, and to enable the tracking force (the force exerted by the stylus upon the record groove) to be set. In pick-up arms designed for high fidelity sound reproduction, all of the component parts of the arm are precision made, since any defects in their manufacture can give rise to undesirable sound distortions.
In the discussion which follows, the pick-up arm according to the present invention will be contrasted with the prior art SME Series II precision pick-up arm which was manufactured by SME Limited of Steyning, Sussex, BN4 3GY, England and has been widely acclaimed as a pick-up arm of exceptionally high quality. The pick-up arm according to the present invention has many constructional details in common with the SME Series II arm, but differs considerably from the latter in regard to its balance weight arrangement.
The balance weight arrangement in the SME Series II arm comprises a main balance weight of cylindrical form which is mounted on the back end of the arm coaxially with the arm and is arranged to translate longitudinally of the arm upon axial rotation of the weight, together with a fine adjustment balance weight which is very much smaller in mass than the main weight and is slidably mounted on one limb of an L-shaped carrier the other limb of which is slidably engaged in a member secured to the back end of the arm. By movement of the fine adjustment balance weight along the first limb, which extends parallel to the arm, the position of the fine adjustment balance weight relative to the arm bearings can be adjusted. By movement of the L-shaped carrier bodily by sliding the other limb thereof into or out of its accommodating bore, the lateral balance of the arm can be adjusted. These and other details of the SME Series II arm will be described in greater detail hereinafter.